RU2743225C1 - Field-effect transistor with schottky barrier - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: disclosed is a field transistor with a Schottky barrier, comprising a semi-insulating substrate, electrodes of a source, a gate, a drain, on the semi-insulating substrate there is an inhomogeneously doped active semiconductor layer of two parts, first and second, first part - at a given distance from the gate electrode, with concentration of dopant greater than 2×10¹⁷ cm^-3 and given surface density of said impurity, second part is between said first part and gate electrode, with dopant concentration of less than 2×10¹⁷ cm^-3, the gate electrode is made on the opposite surface of the active semiconductor layer. Semi-insulating substrate is made from monocrystalline gallium arsenide, said first part of inhomogeneously doped active semiconductor layer is made at distance from gate electrode of more than 0.05 mcm, with thickness of less than 0.07 mcm, with doping impurity surface density (0.6-3.0)×10¹² cm^-2, field transistor with Schottky barrier further includes a buffer and contact layers, wherein buffer layer is made between said semi-insulating substrate and non-uniformly doped active semiconductor layer, with thickness of more than 0.2 mcm, contact layer is made on second part of non-uniformly doped active semiconductor layer, with thickness of more than 0.01 mcm, with concentration of dopant greater than 2×10¹⁸ cm^-3, on its opposite surface there are electrodes of source and drain, distance between borders of contact layer under electrodes of source and drain more than 0.8 mcm, said gate electrode has a length of less than 0.7 mcm, at equal distance from the center between the boundaries of the contact layer under the source and drain electrodes, or is shifted towards the source electrode.

EFFECT: higher amplification coefficient of a field-effect transistor with a Schottky barrier, lower level of low-frequency noise of microwave devices on the MESFET.

1 cl, 3 dwg, 1 tbl

Description

The invention relates to microwave electronics, namely to semiconductor devices, field-effect transistors with a Schottky barrier.

A field-effect transistor with a Schottky barrier (FET) is a field-effect transistor in which the control element is a Schottky barrier at the metal-semiconductor interface.

It is advisable to characterize the reinforcing properties of the PTSh by the steepness of the flow characteristic S - the ratio ΔI _c / ΔU _si , where

I _c - drain current,

U _zi - gate-source voltage.

In this case, the transfer characteristic of microwave devices on the PTSh is linear in the region where the steepness of the transmission characteristic is constant.

Known field-effect transistors with a Schottky barrier with a uniform distribution of the dopant in the active semiconductor layer, providing the required concentration of the main charge carriers and - the flow of electric current when the control voltage is applied. In which the active semiconductor layer is made on a semi-insulating substrate, and on the opposite surface of the active semiconductor layer, the source, gate, drain electrodes are made, while the gate electrode forms a Schottky barrier with the active semiconductor layer [Zi S. Physics of semiconductor devices. M, Mir, 1984, vol. 1 p. 330].

Camiade M. Bert A. Graffeuil J. Pataut G. Low noise FET oscilators // 13 ^th microwave Conf. Dig. 1983, p. 297-302].

Rohdin H. Su C.Y. Sfolte C. A study of the relation between device low-frequency noise and oscilator phas noise for GaAs MESFET's // IEEE MTT-Dig. Conf. 1984, p. 267-269].

The disadvantage of these PTSh is:

first, the low gain in the operating mode and its dependence on the amplitude of the microwave signal due to a decrease in the slope of the PTSh transmission characteristic with an increase in the negative gate-source voltage,

Secondly, a high level of low-frequency noise (at frequencies below 1 MHz) due to the strong dependence of the input capacitance (C _Rin) from the gate-source voltage (U _link), which in turn is caused by the fluctuation of the concentration and mobility of the majority charge carriers in the active semiconductor layer and, accordingly, a high level of low-frequency noise of microwave devices on the PTSh, which limits the use of PTSh in a number of microwave devices, and first of all, in amplifiers and microwave generators.

A field-effect transistor with a Schottky barrier is known, containing a semi-insulating substrate with an active semiconductor layer made on it, on the opposite surface of which the source, gate, drain electrodes are made.

In which, in order to increase the linearity of the transfer characteristic by decreasing the dependence of the slope of the transmission characteristic on the gate-source voltage, the active semiconductor layer is made inhomogeneously doped, while the concentration of the main charge carriers in the active semiconductor layer increases in the direction from the gate electrode to the semi-insulating substrate, or smoothly , or stepwise [Zi S. Physics of semiconductor devices. M, Mir, 1984, vol. 1, p. 348].

The inhomogeneously doped active semiconductor layer made it possible to eliminate the disadvantages characteristic of a PTSh with a uniformly doped active semiconductor layer, but it is not enough in a number of cases of its use in microwave devices.

A field-effect transistor with a Schottky barrier is known, containing a semi-insulating substrate with an active semiconductor layer made on it, on the opposite surface of which the source, gate and drain electrodes are made. In this case, the active semiconductor layer is made, as in the previous analogue, inhomogeneously doped.

In which, as in the previous analogue, in order to increase the linearity of the transfer characteristic, the part of the active semiconductor layer located at a distance from the gate electrode exceeding 0.08 μm is made with a dopant concentration greater than 2 × 10 ¹⁷ cm ^-3 and the surface density of this impurities (1.3-2.5) × 10 ¹² cm ^-2 , and a part of the active semiconductor layer between the said part and the gate electrode is made with a dopant concentration less than 2 × 10 ¹⁷ cm ^-3 [/ Patent 2093925 RF. Field-effect transistor / Bogdanov Yu.M., Pashkovsky A.B. Tager A.S., Yatsyuk Yu.A., Petrov K.I. // Bul. - 1997 - No. 29 /] - prototype.

Optimization of the doping profile of the active semiconductor layer provided a decrease in:

- the dependence of the input capacitance, the slope of the transmission characteristic and the linearity of the transfer characteristic on the gate-source voltage.

- the influence of fluctuations in the concentration and mobility of the main charge carriers in the active semiconductor layer on the parameters of the equivalent circuit of the PTSh and, accordingly, a decrease in the low-frequency noise of the PTSh and microwave devices on the PTSh.

However, when the length of the gate electrode is reduced to less than 1 μm (the typical length of the gate electrode of modern PTSh is less than 0.5 μm) within the stated limits, it is not always possible to provide a region of constant steepness of the transmission characteristic and linearity of the transfer characteristic and, accordingly, a high gain and a low level of low-frequency noise of PTSh and microwave devices on PTSh.

The technical result of the invention is to increase the gain, reduce the level of low-frequency noise of field-effect transistors with a Schottky barrier and microwave devices on them.

The specified technical result is achieved by the claimed field-effect transistor with a Schottky barrier containing a semi-insulating substrate, source, gate, drain electrodes; on the semi-insulating substrate, an inhomogeneously doped active semiconductor layer is made of two parts - the first and the second, the first part - at a given distance from the gate electrode, with with a dopant concentration of more than 2 × 10 ¹⁷ cm ^-3 and a given surface density of this impurity, the second part is between the first part and the gate electrode, with a dopant concentration less than 2 × 10 ¹⁷ cm ^-3 , the gate electrode is made on the opposite surface of the active semiconductor layer ...

Wherein

semi-insulating substrate made of monocrystalline gallium arsenide,

said first part of the inhomogeneously doped active semiconductor layer is made at a distance from the gate electrode of more than 0.05 μm, with a thickness of less than 0.07 μm, with a surface density of the dopant (0.6-3.0) × 10 ¹² cm ^-2 ,

a field-effect transistor with a Schottky barrier additionally contains a buffer and contact layers,

wherein the buffer layer is made between the said semi-insulating substrate and the non-uniformly doped active semiconductor layer with a thickness of more than 0.2 μm,

the contact layer is made on the second part of the inhomogeneously doped active semiconductor layer, with a thickness of more than 0.01 μm, with a dopant concentration of more than 2 × 10 ¹⁸ cm ^-3 , the source and drain electrodes are made on its opposite surface, the distance between the boundaries of the contact layer under the source electrodes and drain more than 0.8 microns,

the said gate electrode is made with a length of less than 0.7 μm, at an equal distance from the center between the boundaries of the contact layer under the source and drain electrodes, or is displaced towards the source electrode.

Disclosure of the essence of the invention.

Performance:

semi-insulating substrate made of monocrystalline gallium arsenide,

the first part of a non-uniformly doped active semiconductor layer at a distance from the gate electrode of more than 0.05 μm, a thickness of less than 0.07 μm, with a surface density of the dopant (0.6-3.0) × 10 ¹² cm ^-2 .

The presence of an additional buffer and contact layers in a field-effect transistor with a Schottky barrier, while when:

a buffer layer is made between said semi-insulating substrate and an inhomogeneously doped active semiconductor layer with a thickness of more than 0.2 μm,

the contact layer is made on the second part of the inhomogeneously doped active semiconductor layer, with a thickness of more than 0.01 microns, with a dopant concentration of more than 2 × 10 ¹⁸ cm ^-3 ,

on its opposite surface, the source and drain electrodes are made, the distance between the boundaries of the contact layer under the source and drain electrodes is more than 0.8 μm,

the gate electrode is made with a length of less than 0.7 μm, at an equal distance from the center between the boundaries of the contact layer under the source and drain electrodes, or is displaced towards the source electrode.

This provides:

firstly, the elimination of migration of uncontrolled impurities from the semi-insulating substrate into the active semiconductor layer, including the channel of the field-effect transistor with the Schottky barrier, and thereby provides:

a) high mobility of the main charge carriers in the active semiconductor layer and, accordingly, an increase in the output current in the channel of a field-effect transistor with a Schottky barrier and, as a consequence, an increase in the PTSh gain,

b) a further decrease in the influence of fluctuations in the concentration and mobility of the majority charge carriers in the active semiconductor layer on the parameters of the equivalent circuit of the PTSh and, as a consequence, a decrease in the low-frequency noise of microwave devices on the PTSh,

secondly, optimization of the design of a field-effect transistor with a Schottky barrier and, thereby, the possibility of selecting for each any length of the gate electrode the corresponding parameters of the active semiconductor layer, ensuring the constancy of the input capacitance when the gate-source voltage changes and at a sufficiently high breakdown voltage (U _pr ) and, thus, an increase in the area of constant steepness of the transmission characteristic (linearity of the transfer characteristic) and, as a consequence, -

firstly, an increase in the PTSh gain,

secondly, a decrease in the level of low-frequency PTSh noise.

And accordingly, the above and in microwave devices on PTSh.

Implementation of the first part of the inhomogeneously doped active semiconductor layer:

at a distance of less than 0.05 μm from the gate electrode, as well as with a thickness of more than 0.07 μm and a surface density of the dopant less than 0.6 × 10 ¹² cm ^{-2, it is} not permissible, due to the emerging strong dependence of the input capacitance and steepness of the transmission characteristic on gate-source voltage.

with a dopant surface density of more than 3.0 × 10 ¹² cm ^{-2 is} not desirable due to:

a) an increase in the cutoff voltage ( _Uoff ) of the PTSh and, accordingly, a drop in its operating voltage,

b) manifestations of edge effects, leading to a stronger dependence of the input capacitance on the voltage at the gate-source electrodes.

Making the buffer layer less than 0.2 μm thick is not desirable due to the loss of its functionality.

The implementation of the contact layer on the second part of the inhomogeneously doped active semiconductor layer with a thickness of less than 0.01 μm, as well as with a dopant concentration of less than 2 × 10 ¹⁸ cm ^{-3, is} undesirable due to an increase in the resistance of the source electrode and, accordingly, a decrease in the PTSh gain.

Making the distance between the boundaries of the contact layer under the source and drain electrodes less than 0.8 μm is undesirable due to a decrease in the breakdown voltage of the PTSh.

The implementation of the gate electrode with a length of more than 0.7 μm is undesirable due to a decrease in the PTSh gain.

So, the set of essential features of the claimed field-effect transistor with a Schottky barrier, in full measure, provides the specified technical result, namely, an increase in the gain, a decrease in the level of low-frequency noise of the PTSh and microwave devices on the PTSh.

The invention is illustrated by drawings.

FIG. 1. A schematic representation of the claimed field-effect transistor with a Schottky barrier is given, where

- semi-insulating substrate made of monocrystalline gallium arsenide - 1,

source, gate, drain electrodes - 2, 3, 4, respectively,

inhomogeneously doped active semiconductor layer - 5, of two parts: the first - 5 a and the second - 5 b.

additional buffer - 6 and contact - 7 layers.

FIG. 2. The implementation of the profile of the concentration of the dopant (donor) impurity along the depth of the active semiconductor layer from the gate electrode is given.

FIG. 3. The dependences of the input capacitance (C _in ) on the gate-source voltage (U _si ) of the declared field-effect transistor with a Schottky barrier (solid line) and a field-effect transistor with a Schottky barrier - prototype (dashed line) are given.

Examples of implementation of the claimed field-effect transistor with a Schottky barrier.

Example 1.

On a semi-insulating substrate made of monocrystalline gallium arsenide - 1 with an atomically smooth surface (AGPCh-76.2-450- (100) 2.5 deg. (110) -EJ-chipboard TU6365-01-52692510-2010) by means of gas-phase epitaxy ( installation AEXTRON) form the following direct sequence of continuous technological layers of a field-effect transistor with a Schottky barrier:

- buffer layer 6 with a thickness of 0.6 μm;

- inhomogeneously doped active semiconductor layer 5 of two parts:

the first 5 a - at a distance from the gate electrode - 0.07 μm, thickness 0.04 μm, with the surface density of the dopant 1.8 × 10 ¹² cm ^-2 ,

the second 5 b - with a dopant concentration of 1.0 × 10 ¹⁷ cm ^-3 ;

- contact layer 7 with a thickness of 0.02 µm, with a dopant concentration of 5 × 10 ¹⁸ cm ^-3 , the distance between its boundaries under the source 2 and drain electrodes 4 is 1.0 µm.

Next, the topology of a field effect transistor with a Schottky barrier is formed by means of lithography and etching methods.

Wherein:

the first part of the inhomogeneously doped active semiconductor layer 5 a is made at a distance from the gate electrode 3 - 0.07 μm,

the contact layer 7 is made on the second part of the inhomogeneously doped active semiconductor layer 5 b, 0.02 μm thick, with a dopant concentration of 5 × 10 ¹⁸ cm ^-3 , on its opposite surface, the source 2 and drain 4 electrodes are made, at a distance between the boundaries of the contact layer 7 under the electrodes of source 2 and drain 4 - 1.0 μm,

the gate electrode 3 is made with a length of 0.3 μm, at an equal distance from the center between the boundaries of the contact layer 7 under the source 2 and drain 4 electrodes.

Examples 2-5.

The examples are made similar to example 1, but with other design parameters of the field-effect transistor with a Schottky barrier, both specified in the claims (examples 2-3) and outside of it (examples 4-5), while when the gate electrode 3 is made at an equal distance from the boundaries of the contact layer 7 under the electrodes of the source 2 and drain 4 (a special case).

Examples 6-10.

The examples are made similarly (examples 1-5) each, respectively, when the gate electrode 3 is displaced towards the source electrode 2 (special case).

Example 6 corresponds to the data of the prototype.

On manufactured samples of a field-effect transistor with a Schottky barrier, the following were measured:

1. PTSh gain at 10 GHz (Agilent Vector Network Analyzer - PNA - L - N5230C).

2. Low-frequency noise (phase noise) of the microwave amplifier on these PTSh at 10 kHz offset from the carrier frequency (Agilent Signal Analyzer - E5052 B - E5052A).

The data are presented in the table and in FIG. 3.

As can be seen from the table, samples of field-effect transistors with a Schottky barrier, made according to the claimed claims, have:

- gain of approximately 11 dB at 10 GHz;

- the level of low-frequency noise of the microwave amplifier on these PTSh at a frequency offset from the carrier frequency of 10 kHz due to the constant input capacitance (Fig. 3) is about 145-155 dB / Hz (examples 1-3, 6-8).

Unlike samples made with design parameters outside the claims, as well as a prototype sample, which have:

- gain 3-10 dB at 10 GHz,

- the level of low-frequency noise of the microwave amplifier on these PTSh at a frequency offset from the carrier frequency of 10 kHz is about 125-140 dB / Hz (examples 4-5, 9-10).

Thus, the declared field-effect transistor with a Schottky barrier in comparison with the prototype will provide:

- an increase in the gain by about 80 percent,

- decrease in the level of low-frequency noise of microwave devices on the declared PTSh by about 10-20 dB / Hz.

Claims (1)

A field-effect transistor with a Schottky barrier, containing a semi-insulating substrate, source, gate, drain electrodes, a non-uniformly doped active semiconductor layer is made on the semi-insulating substrate from two parts - the first and the second, the first part - at a given distance from the gate electrode, with a dopant concentration of more than 2 × 10 ¹⁷ cm ^-3 and a given surface density of this impurity, the second part is between the said first part and the gate electrode, with a dopant concentration less than 2 × 10 ¹⁷ cm ^-3 , the gate electrode is made on the opposite surface of the active semiconductor layer, characterized in that that the semi-insulating substrate is made of monocrystalline gallium arsenide, the said first part of the inhomogeneously doped active semiconductor layer is made at a distance from the gate electrode of more than 0.05 μm, with a thickness of less than 0.07 μm, with a surface density of the dopant (0.6-3.0) × 10 ¹² cm ^-2 , a field-effect transistor with a Schottky barrier complement separately contains a buffer and contact layers, while the buffer layer is made between the aforementioned semi-insulating substrate and an inhomogeneously doped active semiconductor layer with a thickness of more than 0.2 μm, the contact layer is made on the second part of an inhomogeneously doped active semiconductor layer with a thickness of more than 0.01 μm, with with a dopant concentration of more than 2 × 10 ¹⁸ cm ^-3 , the source and drain electrodes are made on its opposite surface, the distance between the boundaries of the contact layer under the source and drain electrodes is more than 0.8 μm, the said gate electrode is made less than 0.7 μm long, equal distance from the center between the boundaries of the contact layer under the source and drain electrodes, or is displaced towards the source electrode.

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